Still getting used to moving the desk for/backward instead of my chair...

I used this axonometric drawing to explain the 4 ft x 4 ft frame to the welder (casters are welded to the steel frame) and the base Sketch-up model is available in Google 3D warehouse. Added two cross braces (2 in angle bar) at the bottom for stability, and so that each side of the desk has its own footrest.